Having been involved in the pigging industry for the last 12+ years, I have seen this on occasion, probably due to one of the following:
– an overly agressive pigging operator
– OR which would be the case if using our technology, these shavings may be filings from the ‘sacrificial’ appendages used when pigging close to the tube wall. We (and I think all the others in the industry) when pigging at full ID, use appendages that are softer than the tube material in order to mitigate the chance of tube scoring.
– OR which I personnaly have observed, is that the heater design incorporates u-bends with heavier wall thickness than the tubes, so there is some extra material to compensate for high velocity errosion when using SAD or on-line spalling. (eg: schedule 40 tubes with schedule 80 u-bends) With this smaller ID in the u-bends, it is extremely difficult to remove coke to the tube ID without some scoring of the u-bends.
It would obvioulsy be in everybodies best interest to discuss this with your pigging company rep.
For the record, our company does not work in North America yet, so I doubt I am defending our group.
Please feel free to call if I can be of any assistance.
Critical Path Decoking Technology